Early dysfunction of iris sensory fibres in diabetic patients.

Background: The present study was designed to propose transcutaneous electrical nerve stimulation (TENS) of the infratrochlear nerve as a noninvasive test useful in the detection of early iris small nerve fibre dysfunction in patients with diabetes mellitus.

Methods: A total of 32 diabetic patients with no symptoms or signs of diabetic neuropathy were enrolled from a clinical practice. Sixteen of them, 6 women and 10 men, ranging in age from 19 to 53 years, had been affected by IDDM for 13 +/- 2 years. The remainder, 6 women and 10 men, age range 32 to 58 years, were suffering from NIDDM (duration of manifestation 5 +/- 1 years). Twenty-six healthy individuals, 11 women and 15 men, ranging in age from 21 to 47 years, served as controls. Pupil area changes induced by TENS of the infratrochlear nerve were investigated. The electrical stimulus was not painful and consisted of a single square wave pulse of 40 mA intensity and 0.8 ms duration. Measurements were carried out by means of a TV monocular electronic pupillometer.

Results: A clear-cut miosis was provoked in controls (p < 0.01 versus basal values 100 sec to 220 sec from stimulation). NIDDM patients also showed a miotic response, but it was slower in onset (p < 0.05 versus basal values 140 sec after stimulation) and shorter (p < 0.01 at 180 sec from stimulation) in duration. No pupillary changes were registered in IDDM patients.

Conclusions: An abnormality of iris sensory nerve fibres in inducing pupillary constriction was detected in both diabetic groups. The differences in the severity of the dysfunction could be related to the differences in duration of the disease among the diabetic patients in the two groups. In conclusion, TENS of the infratrochlear nerve could represent an original noninvasive method in detecting early iris sensory alterations in diabetic patients.